1. Field of the Invention
This invention relates to new photoacid generator (xe2x80x9cPAGxe2x80x9d) systems and photoresist compositions that comprise such systems. PAG systems of the invention in, general comprise one or more photoacid generator compounds and one or more sensitizer compounds. PAGs of the invention are preferably employed in resists imaged at short wavelengths, such as sub-200 nm, e.g. 193 nm and 157 nm.
2. Background
Photoresists are photosensitive films for transfer of images to a substrate. They form negative or positive images. After coating a photoresist on a substrate, the coating is exposed through a patterned photomask to a source of activating energy such as ultraviolet light to form a latent image in the photoresist coating. The photomask has areas opaque and transparent to activating radiation that define an image desired to be transferred to the underlying substrate. A relief image is provided by development of the latent image pattern in the resist coating. The use of photoresists is generally described, for example, by Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975), and by Moreau, Semiconductor Lithography, Principals, Practices and Materials, Plenum Press, New York (1988).
Known photoresists can provide features having resolution and size sufficient for many existing commercial applications. However for many other applications, the need exists for new photoresists that can provide highly resolved images of submicron dimension.
Various attempts have been made to alter the make-up of photoresist compositions to improve performance of functional properties. Among other things, a variety of photoactive compounds have been reported for use in photoresist compositions. See, e.g., U.S. Pat. No. 4,450,360 and European Application 615163.
More recently, certain xe2x80x9cchemically amplifiedxe2x80x9d photoresist compositions have been reported. Such photoresists may be negative-acting or positive-acting and rely on multiple crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In other words, the photogenerated acid acts catalytically. In the case of positive chemically amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain xe2x80x9cblockingxe2x80x9d groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,851; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon selective cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is provided, e.g., carboxyl, phenol or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer.
We have now discovered novel photoacid generator systems for use in either positive-acting or negative-acting photoresist compositions.
We have found that excessive absorbance can remain an issue for resists imaged at short wavelengths such as 193 nm, even where the resist resin is optimized for low absorbance such as by having little or no aromatic content. In particular, we have found that a targeted absorption xe2x80x9cbudgetxe2x80x9d for a short wavelength resist may be substantially consumed by the resin component alone.
Photoacid generator systems of the invention in general comprise one or more photoacid generator compounds and one or more sensitizer compounds. The sensitizer component can be integral (covalently linked) to another resist component, such as the resin or PAG, but more typically the sensitizer is a separate resist additive.
Preferred sensitizer compounds are aromatic systems, both heteroaromatic and carobcyclic aryl, including compounds that comprise separate and/or fused multi-ring aromatic systems. Preferred sensitizer compounds are electron rich and comprise one or more electron-donating substituents, such as e.g. optionally substituted alkyl preferably having 1 to about 20 carbon atoms, optionally substituted alkoxy preferably having 1 to about 20 carbon atoms, optionally substituted thioalkyl preferably having 1 to about 20 carbon atoms, optionally substituted thioalkoxy preferably having about 1 to 20 carbon atoms, hydroxy, optionally substituted thiohydroxyalkyl preferably having 1 to about 20 carbon atoms, and the like. Exemplary preferred sensitizer compounds are discussed below.
Sensitizer compound(s) can be employed in a resist in quite small amounts and thus can positively impact efficiency (i.e. photoacid generation) of the PAG component without unduly adding to the overall absorbance of the resist.
In fact, it has been found that addition of a sensitizer component can dramatically increase the sensitivity of a PAG component to short wavelength radiation, particularly sub-200 nm radiation such as 193 nm.
Preferred PAGs for use in the PAG systems of the invention can exhibit good transparency without significant loss of photoacidgeneration efficiency upon exposure to short wavelength radiation such as 193 nm.
Preferred PAGs for use in the PAG systems of the invention include sulfonium and iodonium compounds having a cation component that comprises one or more substituents of naphthyl, thienyl, or pentafluorophenyl, or a cation component that has a sulfur ring group such a thienyl, benzothiophenium, etc. Those substituents (chromophores) provide enhanced transparency of the PAG, while maintaining effective photoacid generation properties.
Additional preferred PAGs for use in the PAG systems of the invention include oxime sulfonate PAGs, preferably where the oxime carbon has one or two electron-withdrawing substituents. Also preferred are N-oxy-imidosulfonate PAGs that preferably contain contain two or more N-oxyimidosulfoanate groups in a single PAG compound. Such compounds are capable of generating a molar excess of photogenerated acid per mole of the PAG compound.
Preferably, PAGs of the invention are used in positive-acting or negative-acting chemically amplified photoresists, i.e. negative-acting resist compositions which undergo a photoacid-promoted crosslinking reaction to render exposed regions of a coating layer of the resist less developer soluble than unexposed regions, and positive-acting resist compositions which undergo a photoacid-promoted deprotection reaction of acid labile groups of one or more composition components to render exposed regions of a coating layer of the resist more soluble in an aqueous developer than unexposed regions. Ester groups that contain a tertiary non-cyclic alkyl carbon or a tertiary alicyclic carbon covalently linked to the carboxyl oxygen of the ester are generally preferred photoacid-labile groups of resins employed in photoresists of the invention.
As discussed above, preferred imaging wavelengths of photoresists of the invention include sub-200 nm wavelengths e.g. 193 nm and 157 nm.
Particularly preferred photoresists of the invention contain an imaging-effective amount of one or more PAGs (including PAGs of the below-discussed formulae) that is selected from the group of:
1) a phenolic resin that contains acid-labile groups that can provide a chemically amplified positive resist particularly suitable for imaging at 248 nm. Particularly preferred resins of this class include: i) polymers that contain polymerized units of a vinyl phenol and an alkyl acrylate, where the polymerized alkyl acrylate units can undergo a deblocking reaction in the presence of photoacid. Exemplary alkyl acrylates that can undergo a photoacid-induced deblocking reaction include e.g. t-butyl acrylate, t-butyl methacrylate, methyladamantyl acrylate, methyl adamantyl methacrylate, and other non-cyclic alkyl and alicyclic acrylates that can undergo a photoacid-induced reaction; such polymers have been described in U.S. Pat. Nos. 6,042,997 and 5,492,793, incorporated herein by reference; ii) polymers that contain polymerized units of a vinyl phenol, an optionally substituted vinyl phenyl (e.g. styrene) that does not contain a hydroxy or carboxy ring substituent, and an alkyl acrylate such as those deblocking groups described with polymers i) above, such as polymers described in U.S. Pat. No. 6,042,997, incorporated herein by reference; and iii) polymers that contain repeat units that comprise an acetal or ketal moiety that will react with photoacid, and optionally aromatic repeat units such as phenyl or phenolic groups, such as polymers as described in U.S. Pat. Nos. 5,929,176 and 6,090,526, incorporated herein by reference.
2) a resin that is substantially or completely free of phenyl or other aromatic groups that can provide a chemically amplified positive resist particularly suitable for imaging at sub-200 nm wavelengths such as 193 nm. Particularly preferred resins of this class include: i) polymers that contain polymerized units of a non-aromatic cyclic olefin (endocyclic double bond) such as an optionally substituted norbornene, such as polymers described in U.S. Pat. Nos. 5,843,624 and 6,048,664, incorporated herein by reference; ii) polymers that contain alkyl acrylate units such as e.g. t-butyl acrylate, t-butyl methacrylate, methyladamantyl acrylate, methyl adamantyl methacrylate, and other non-cyclic alkyl and alicyclic acrylates; such polymers have been described in U.S. Pat. No. 6,057,083; European Published Applications EP01008913A1 and EP00930542A1; and U.S. pending patent application Ser. No. 09/143,462, filed Aug. 28, 1998, all incorporated herein by reference; iii) and polymers that contain maleic anhydride.
Resists of the invention also may comprise a mixture of distinct PAGs, typically a mixture of 2 or 3 different PAGs, more typically a mixture that consists of a total of 2 distinct PAGs. Photoresists that contain such PAG mixtures can exhibit even further enhanced lithographic performance.
The invention also provide methods for forming relief images of the photoresists of the invention, including methods for forming highly resolved patterned photoresist images (e.g. a patterned line having essentially vertical sidewalls) of sub-quarter micron dimensions or less, such as sub-0.2 or sub-0.1 micron dimensions.
The invention further provides articles of manufacture comprising substrates such as a microelectronic wafer or a flat panel display substrate having coated thereon the photoresists and relief images of the invention. Other aspects of the invention are disclosed infra.